1. Field of the Invention
This invention relates to microstereoscopes and the like, and more particularly to spot illumination systems therefor.
2. Description of the Prior Art
As is well known, a photointerpretation stereoscope is a device having rotatable rhomboid arms for movement over film strips placed on the viewing plate of an interiorly illuminated box. Such illumination, which is from a number of fluorescent lamps, may be of the order of 3,000-5,000 foot lamberts, is sufficient for background lighting for orientation purposes, but is not bright enough for detailed inspection of minute film areas in many instances. For such spot detail work, one needs much higher intensity illumination, e.g., 30,000-50,000 ft. lb.
Considerable time, effort and expense have been devoted to developing means for effecting such high intensity spot illumination via small lamps and structures for rotating them in synchronism with the rhomboid arms. However, such lamps are additional heat sources which require attendant blowers and associated cooling equipment. Such heat sources adjacent the viewing plate are undesirable because of the deleterious efforts of the high temperatures on the glass of the viewing plate and the film placed thereon. Also, vibrations set up by the blowers have the undesirable effect at high power magnification of degrading the images being viewed. Further, such lamps are not readily accessible for replacement purposes, e.g., requiring the viewing plate to be lifted off the light box in order to get to the bulbs.